There are many procedures associated with the oral cavity in which a precise three-dimensional representation of the cavity is very useful to the dental practitioner. Herein, “practitioner” refers to any one of a dentist, dental surgeon, dental technician, orthodontist, prosthodontist, or any other caregiver that may be involved in determining, preparing or providing dental treatment to a patient, particularly orthodontic treatment.
Such representations enable the practitioner to study the cavity of individual patients in a similar manner to the study of the traditional plaster model. More importantly, three-dimensional numerical entities of the dental cavity also allow the practitioner to study alternative methods or approaches when dealing with particular dental problems of any given patient. For example, in orthodontics, a computer model of a patient's teeth may be manipulated to arrive at the optimal arrangement for brackets to ensure effective treatment of crooked teeth. For such procedures, it is often useful to provide a three-dimensional representation of the individual teeth, each of which can be moved independently in a computer simulation of the orthodontic treatment plan and orthodontic record. Hitherto, identification and separation of the data sets representative of the individual teeth has been performed manually.
In U.S. Pat. No. 6,739,869, assigned to the present Assignee, a method for virtual orthodontic treatment is disclosed in which a virtual set of orthodontic components is associated, in a virtual space, with a first virtual three-dimensional image of teeth, and then by a set of rules which define the effect of the set of components' teeth, the effect of the virtual treatment can be computed. This virtual treatment can be used to predict the results of a real-life orthodontic treatment as to design such a treatment.
Another procedure relates to the manufacture of a dental prosthesis, such as a crown or bridge, which requires the finish line, or transition boundary between the prosthesis and the dental preparation to be precisely defined in three-dimensions. Obtaining the finish line coordinates from a computer model is more efficient and often more accurate than from a plaster cast, and moreover facilitates the production of such a prosthesis, for example via CNC machining, rapid prototyping, or other computerised technologies, if desired.
There are also procedures in which particularly good three-dimensional definition of a large area of the intraoral cavity is required, and it may be necessary at times to scan parts of the cavity sequentially and then “stitch” the various data sets together. Thus, surface topologies of adjacent portions, at times from two or more different angular locations relative to the structure, are determined and the topologies are combined, in a manner known per se. In practice, such stitching is usually performed automatically, by identifying a surface profile or topography corresponding to at least part of the data of one data set that is substantially identical to that of another data set. The data sets are then manipulated such as to match the coordinates of the surface profile between the data sets to obtain a larger numerical entity comprising these data sets in their proper spatial relationship. However, the data sets often include surface data relating to the soft tissues such as gums, cheeks and tongue, for example, which may distort and move while the different scans are performed. This relative movement makes the stitching procedure more problematic, since parts of the data sets thus obtained will never synchronise, even though they relate to overlapping portions of the intra-oral cavity.
In procedures relating to the manufacture of a dental prosthesis such as a crown or bridge, or in other dental restorations, it is important to match the color and texture of the prosthesis with that of the surrounding teeth in the vicinity of the target area in which the prosthesis is to be implanted, to give the prosthesis or restoration a natural appearance. Traditional methods of color matching are based on visual comparison between a removable tooth-shaped color tab of a shade guide, such as for example Vita, and the surrounding teeth. The practitioner can then choose the standard shade that best matches the overall color of the other teeth. The appropriate shade reference can then be communicated to the laboratory that is to manufacture the prosthesis. Similar matching methods are routinely employed for enabling the color of filler material to be matched to the tooth that requires a filling. It should be noted that unlike the tooth shades from the shade guides, which are uniform in color, a tooth have many different shades. For example, tooth stains and the like alter then tooth's color locally. Attempts have been made at providing a more exact match. For example in U.S. Pat. No. 5,800,164 a system is described for the selection of form and color structure of teeth, and includes several assortments of models and representations as well as layering diagrams of different tooth forms and color structures. A comparison of form and color structure between the patient's teeth and the models is made, and a suitable assortment is selected. The layering diagrams thus produced enable the production of the prosthesis to be carefully controlled to provide the desired form and color structure. In U.S. Pat. No. 4,836,674 a method and apparatus are described for obtaining the best color match with respect to adjacent teeth, for different lighting conditions, but considers only the overall color of the teeth, and does not address local variations of color in the teeth. In U.S. Pat. No. 6,525,819, a calorimeter is provided for providing, inter alia, the one-dimensional array of color data along a line on the surface of the intra-oral cavity, including the teeth. In U.S. Pat. No. 5,766,006 a method is described for comparing the tooth shade after the patient's teeth are whitened, in which a color two-dimensional image of the tooth is obtained before the whitening, comparing the color information representative of the color of the tooth, and identifying one or more tooth shades with a combined color corresponding to the color of the tooth. After whitening the tooth, another image is taken thereof and compared to the image before whitening.
Other US patents of general background interest include the following.
In U.S. Pat. Nos. 5,851,113, 5,871,351, 6,118,521, 6,239,868, 6,246,479, 6,417,917, 6,538,726, 6,570,654 and 6,573,984 color measuring systems and methods such as for determining the color or other characteristics of teeth are disclosed, in which these characteristics are obtained using a fibre optics arrangement which is targeted onto a specific area of each tooth and at a certain height and angle with respect to this area. The color measurement data obtained may be used to implement processes for forming dental prostheses.
In U.S. Pat. No. 6,007,332, a method and system for determining the color characteristic of a tooth employs the photographic imaging of the tooth, and the photographing of visually selected color standards, to achieve the final selection of the closest color match. The resulting photographic images, which may be on a single photograph, are subjected to calorimetric or spectrophotometric analysis to achieve the final selection of the closest match.
In U.S. Pat. No. 6,030,209, a spectrophotometer device measures and provides general colorimetric data regarding hue, chroma, value, and translucency for each of the incisal, middle, and cervical regions of the tooth. This calorimetric data is then converted via an algorithm to a recipe that the dentist or dental technician follows in constructing a dental restoration. A porcelain system is also provided which allows a user to independently alter one color component while not affecting the other three color components.
In U.S. Pat. No. 6,033,222, a fabrication method for dental translucent restorations involves forming a dental die from impression of tooth stump, in which a series of die spacers of differing shades are used to match or replicate an assortment of tooth stump or dentin tooth shades. The method comprises applying color and shade to match dentist's prescription, forming a dental wax-up and then the dental structure.
In U.S. Pat. Nos. 6,190,170, and 6,238,567, an automated tooth shade analysis and matching method is used for making a dental prosthesis. An image of the teeth is acquired including black and white normalization references for determining absolute black and absolute white within the image. The image is normalized in accordance with the normalization references, and then standardized by matching the pixels of the normalized image to selected shade standards for the prosthesis.
In U.S. Pat. No. 6,379,593, a method for producing a multi-colored dental restoration is disclosed. A compacting die is filled with a matrix of two or more plastics materials of different colors, and the pressure is applied to the matrix in the die.
The 3D surface structure of the teeth is not considered in any of the aforesaid patents.